Drill bit percussor apparatus

ABSTRACT

A drilling fluid actuated drill bit percussor for insertion in a drill string having a reciprocating hammer which is periodically raised by an increase in drilling fluid pressure therebelow and is accelerated downward by hydrostatic pressure and by the force of a contracting vacuum chamber which chamber was expanded during upward hammer movement.

United States Patent 3 1 3,602,317

[72] Inventor ElvaJ.Scrogglns [56] 'ReferencesCited I Lafayette, -9 v UNITED STATES PATENTS [2U P 872551 2,758,817 8/1956 Bassinger 91/50x 451 Patented Aug.31 1971 "m 73 A Mm C t n 2,943,603 7/1960 Bass1nger-. 91/5ox l 1 ssgnee H 3,387,671 6/1968 0611161.... 173/73 F 3,403,739 10/1968 Brown 173/73 Primary Examiner-Stephen J. Novosad AnomeysPaul E. Harris and Lee R. Larkin [541 mum. BIT PERCUSSOR APPARATUS claimss Drawing Figs ABSTRACT: A drilling fluid actuated drill bit percussor for [52] US. Cl 173/73, insertion in a drill string having a reciprocating hammer which 173/131, l73/132 is periodically raised by an increase in drilling fluid pressure [5 1] Int. Cl EZlb 1/06 therebelow and is accelerated downward by hydrostatic pres- [50] Field of Search 91/50; sure and by the force of a contracting vacuum chamber which 173/73, 131,132 chamber was expanded during upward hammer movement.

- 514 I 4! r .I I l .1 30/ i /9 1 ..p- I 8 I R l 44 v /7 l 45 -/a' z 5/ 3 ;I a; //-2J 1 i tI 5 I l d? 1 20 I i $2 I 2 33- \Q I 7\\ i Ja I 5: 1 I :3; [a A a F /l i i 6/ M V f r- 64- ,1 l I I 4 I I I g 9 l i E 3 I /*1 v i 17 r l Jo 1 DRILL BIT PERCUSSOR APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a drilling fluid actuated reciprocating piston drill bit percussor for insertion in a drill string.

2. Description of the Prior Art It is well known in the drilling art that extremely hard subsurface formations can be drilled more readily by applying a repetitive downward percussive blow to a rotational drill bit. Some prior art devices used for this purpose require multiple sources of actuation fluid to drive the percussive device. Other devices utilize pressurized drilling mud to actuate the hammer, but completely interrupt the flow of drilling mud during operation, thereby preventing continuous flushing of the borehole. Some prior art devices arenot self-contained, requiring that an additional part or parts be" transmitted through the drill string to the device when it is desired to actuate the device. Many of the prior art devices discussed above utilize multiple valving systems and have a large number of moving parts, making the devices susceptible to frequent failure when subjected to continuous high pressure operation.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved percussive hammer apparatus which is operable from the normal supply of drilling fluid, which provides a continuous flow of drilling fluid to the drill bit, and which is less susceptible to malfunctioning because of simplicity of construction.

Briefly stated, this invention relates to an improved downhole apparatus for imparting a percussive force to a drill bit which is operated by the normal downwardly flowing drilling fluid. A housing having an axial drilling fluid passageway therethrough is arranged for connection to a drill string and carries an anvil at the lower end thereof, which anvil supports a drill bit therebelow. A generally tubular reciprocating hammer is mounted above the anvil and is raised by increased drilling fluid pressure therebelow, which pressure is caused by the closing of a partial check valve. The upwardly moving hammer unseats the check valve, which releases the upward pressure on the hammer and allows the hammer to fall downward. The hammer is accelerated downward by hydrostatic pressure, by the force of a contracting vacuum chamber, which chamber was expanded during the upward hammer movement, and by the imbalance of imbalance pressure upon the upward and downward end surfaces provided on the hammer assembly.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. IA is a central vertical sectional view showing the top portion of one preferred embodiment of the invention.

FIG. 1B is a continuation of FIG. 1A and is a central vertical sectional view showing the lower portion of this embodiment.

FIG. 2 is a sectional view taken along line 2-2 of FIG. 18.

FIG. 3 is a partial central sectional view showing in greater detail the preferred embodiment of the valve portion of the invention.

FIG. 4 is a partial central sectional view showing an alternate embodiment of the valve portion of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the upper and lower portions of the apparatus of this invention are shown in FIGS. 1A and 18, respectively, with part of a conventional collar illustrated in broken lines at the top of FIG. IA and part of a conventional drill bit 11 illustrated in broken lines at the bottom of FIG. 18.

As shown in FIG. 1A, the invention includes a housing generally designated by the numeral 9 and including a generally tubular housing sleeve 12 threadably secured to a top sub 13, which in turn is threadably secured to the lower end of a drill collar I0, thereby providing means to support the tool near the lower end of a drill string. Top sub 13 is provided with a central axial bore M therethrough, which is arranged to receive tubular shaped mandrel l5 thereon. Bore 14 has an upwardly facing counter bore portion 16 providing a seat for generally cylindrical mandrel nut 17 which is threaded on the upper end of mandrel I5. Mandrel I5 and nut 17 are provided with wrench splines I8 and wrench detents 19, respectively, to facilitate assembly of the tool. The depth of counter bore I6 is larger than the thickness of nut I7 and is slightly larger in diameter than nut l7 so that mandrel [5 may slide axially a small distance with respect to top sub 13 during operation of the tool. The downward axial movement of mandrel I5 is limited by nut 17 seating in counter bore 16 and is limited in upward movement by the surface of nut 17 striking the lower end ofdrill collar 10.

Mandrel 15 has an axial passageway 20 therethrough for the downward flow of drilling fluid from the drill string. Mandrel l5 depends coaxially into housing sleeve 12 and forms an annular chamber 21 therewith, with ports 22 and 23 through top sub I3 and housing sleeve 12, respectively, providing means for the free flow of drilling fluid between chamber 21 and the exterior of the tool during operation.

Mandrel I5 is provided with an enlarged lower outside diameter forming a radially outwardly extending upwardly facing annular shoulder 24 thereabout. In cooperation with an opposing shoulder 31 on hammer assembly 29 of the tool, described in greater detail below, the opposing shoulders and circumferential surfaces of the mandrel and hammer assembly form an annular vacuum chamber 32 which is enlarged as hammer assembly 29 raises and is subsequently collapsed to accelerate hammer assembly 29 downward during the power stroke thereof.

Hammer assembly 29 is slidably positioned in chamber 21 about the lower portion of mandrel 15 and includes packing nut 25, packing sleeve 26, central hammer sub 27 and bottom hammer sub 28, with threaded connections provided between adjacent parts of the assembly. Hammer assembly 29 has a central axial passageway 30 therethrough in alignment with passageway 20 through mandrel 15, thereby permitting the uninterrupted downward flow of drilling fluid from the drill collar 10 through hammer assembly 29 and isolating the upper surface of hammer assembly 29 from the downward flow of drilling fluid through the drill string.

The inside diameter of the lower portion of passageway 30 in hammer assembly 29 is larger than the inside diameter of the upper portion thereof, forming a radially outwardly extending downwardly facing annular shoulder 31 therein, which shoulder cooperates with shoulder 24 about mandrel I5 to form annular chamber 32 therebetween.

Upper and lower annular packings 33 and 34 are provided between the hammer assembly 29 and mandrel I5 above and below chamber 32, respectively, so that a partial vacuum will be maintained in chamber 32 when the hammer assembly 29 moves upward relative to mandrel 15 during operation. Means are provided conveniently in the form of radial bore 35 and set screw 36 in hammer assembly 29 so that chamber 32 may be evacuated during assembly.

Central sub section 27 of hammer assembly 29 has a reduced external diameter at the lower end, forming annular shoulder 38 thereabout, which shoulder acts as one of the force transmitting surfaces of hammer assembly 29 during operation, as described below.

The reduced diameter of sub 27 of the lower portion of hammer assembly 29, combined with the enlarged passageway 30 of hammer assembly 29, causes the efi'ective lower surface area of hammer assembly 29 to be less than the effective upper surface area thereof. Since both surfaces are effectively subjected to substantially the same hydrostatic drilling fluid pressure during the downward stroke of the hammer assembly, as described below, this differential in area causes a net downward acceleration of the hammer assembly, increasing its momentum and the magnitude of the percussive force it can deliver. The outer circumferential surface of sub 27 and the adjacent inner circumferential surface of the housing sleeve 12 are provided with cooperative splines 39 and 40, respectively, to prevent relative rotational movement therebetween during operation.

Referring to the upper portion of FIG. 1B, the external diameter of sub 27 is further reduced, forming annulus 42 with housing sleeve 12. Slidably positioned in annulus 42 beneath shoulder 38 is a generally tubular shaped sleeve 43 which acts in cooperation with hammer assembly 29 as a force transmitting means for transferring the downward momentum of hammer assembly 29 into a percussive blow upon the drill bit during operation, as described below. Because of this cooperation in delivering a percussive blow to the bit, sleeve 43 may sometimes be referred to as a lower telescoping portion of the hammer assembly.

A circumferential groove 44 is provided about the outer surface of sleeve 43 and forms annulus 45 with housing sleeve 12. Removable plugs 46 and 47 in housing sleeve 12 close conduits which communicate with annulus 45 and allow access for filling it with lubricant. Similarly, threaded plugs 48 and 49 are mounted in sleeve 43 and close conduits communicating with annulus 42, providing means to fill annulus 42 with lubricant during assembly.

Sleeve 43 also acts in cooperation with hammer assembly 29 during the upward movement thereof to unseat the valve portion of the tool as hereinafter described. The center of sleeve 43 has a radially inwardly extending annular portion forming annular lug 50 which projects into annulus 42, as shown in FIG. 1B. Bottom sub 28 is provided with an upwardly facing shoulder 51 which is arranged to strike the lower surface of lug 50 when hammer assembly 29 moves upward during operation and approaches its upper limit of travel, thereby carrying sleeve 43 upward therewith.

Referring now to the lower portion of FIG. 1B, the lower end of housing sleeve 12 is threaded to a generally tubular bot tom connector sub 52 which is provided with axial splines 53 extending radially inward from the lower inside circumferential surface thereof. The upper end of bit connector 54, having cooperating axial splines 55 extending radially outward from the outside surface thereof, is slidably disposed within sub 52 and is provided with a central axial drilling fluid flow passageway 56 therethrough of approximately the same diameter as passageway 30 through hammer assembly 29. The arrangement of the splined slidable connection between sub 52 and connector 54 is shown in detail in FIG. 2.

Referring again to FIG. 18, a generally tubular shaped anvil 57 (having a frustoconical shaped valve seat 58 formed about the upper end thereof) is threadable secured to the upper end of connector 54 and acts as a stop nut to limit the axially slid ing downward movement of connector 54 relative to sub 52. A compression spring 59, seated in matching circumferential grooves 60 and 61 in sub 52 and connector 54, respectively, is arranged to urge connector 54 downward relative to sub 52. Spring 59 is of sufficient strength to force connector 54 and attached drill bit 11 downward relative to sub 52 when there is no upward weight upon bit 11, as for example when the drill string is being inserted into or removed from the borehole.

Referring now to FIG. 3, which is an enlarged view of the central portion of FIG. 18, a preferred embodiment of the valving mechanism of the tool will be described in detail. The valving mechanism is utilized to alternately restrict and relieve the downward flow of drilling fluid through the tool, thereby creating cyclical drilling fluid pressure increases below the hammer assembly which force the hammer assembly upward in preparation for its downward power strokes.

Valve 62, having a central valve stem 63 extending axially upward therefrom, is slidably positioned above anvil 57 and is provided with a chamfered valve seat 64 about the lower end thereof formed to mate with valve seat 58 on anvil 57. A central axial drilling fluid passageway 65 is provided through valve 62 and valve stem 63 in alignment with passageway 30 thereabove and passageway 56 therebelow, which allows drilling fluid to continuously flow through the tool and into the borehole therebelow during drilling.

An insert'66 is seated in the upper end of passage 65 and is retained therein by nut 67 which is threaded to the upper end of valve stem 63. The cross-sectional area of the opening in insert 66 is less than the cross-sectional area of passageway 30 thereabove, whereby a pressure differential is established in the drilling fluid across valve 62 when valve 62 is seated with anvil 57 and drilling fluid is flowing downwardly through the tool.

Lifting means for unseating valve 62 as hammer assembly 29 approaches its upper limit of travel is operably connected between sleeve 43 and valve 62 and includes a valve carrier 68 having a plurality of axially extending drilling fluid passageways'69 therethrough. Carrier 68 is slidably mounted about valve stem 63 and retained thereon by nut 67. Passageways 69 allow drilling fluid to flow from passageway 30 above valve 62 to passage 56 therebelow when valve 62 is unseated from anvil 57. A compression spring 70 positioned in matching circumferential grooves 71 and 72 in valve carrier 68 and valve 62, respectively, acts to continually urge valve 62 downward relative to valve carrier 68. When the valve assembly moves downward during operation and approaches contact with anvil 57, spring 70 acts as a shock absorber to prevent a rigidly forced seating of valve 62 against anvil 57.

A portion of the valve lifting means is rigidly connected to sleeve 43 and includes a generally tubular shaped hammer nose 73 threaded to the lower end of sleeve 43. Nose 73 is provided with a rounded lower end surface for striking anvil 57 to deliver the percussive force from hammer assembly 29 thereto. The inner circumferential surface of hammer nose 73 has an upward and outward conical taper which acts as a seat for valve carrier spring support 74, slidably held therein.

Compression spring 75 is positioned between valve carrier 68 and spring support 74 and acts to continually urge valve carrier 68 upward relative to sleeve 43. A snap ring 76 provided on the lower inside circumferential surface of sleeve 43 acts to limit the upward movement of valve carrier 68 and valve 62 relative to sleeve 43.

In order to prevent the downward movement of sleeve 43 and the valve assembly from continuing in contact with anvil 57 when drill bit 11, connector 54 and anvil 57 move downward relative to housing 12 (as for example, when the drill string is inserted into or removed from the bore hole), a ring shaped antistall skirt 77 is threaded to hammer nose 73 and extends downward therefrom operational reasons the upper end of sub 52. After the skirt-valve-sleeve assembly has followed the anvil-bit assembly downward a short distance, skirt 77 contacts sub 52, terminating the relative movement therebetween. When weight is taken off bit It, anvil 57, connector 54 and bit 11 continue to move downward until the upper end of splines 53 on sub 52 contact the lower end surface of anvil 57. In this extended position, valve 62 is unseated from anvil 57, allowing the relatively unrestricted downward flow of drilling fluid therebetween and preventing a hammer raising pressure buildup beneath hammer assembly 29. For the operational reasons described below, the effective upper surface area of valve 62 is made equal to the effective lower surface area of sleeve 43.

In operation, the percussion tool is threadably connected to drill collar 10 on the lower end of a drill string and drill bit 11 is threadably secured to connector 54. As the tool is lowered into the borehole, spring 59 forces connector 54, anvil 57 and bit 11 downward relative to the housing. Hammer assembly 29 and sleeve 43 are also in their lowermost position, with the bottom of antistall skirt 77 resting on the top end of sub 52. In this position, valve 62 is unseated from valve seat 58 on anvil 57 and drilling fluid in the bore hole may flow upward through the bit ill into the tool and drill string thereabove. When bit 11 reaches the bottom of the hole, the weight of the drill string compresses spring 59, and valve 62 will be initially seated upon seat 58 of anvil 57.

As pressurized drilling fluid, such as a mud composition, is forced downwardly through thedrill string and tool, the tool will begin to function. The drilling fluid may be pumped into Operation of the alternate embodiment valve assembly shown in FIG. 4 is similar to that described above. Referring to FIG. 4, as the pressure of the drilling mud increases above be flowing downwardly through the tool and through the orifree or insert 66. The restricting effect of insert 66 causes a drilling fluid pressure buildup in the space above valve 62 and beneath hammer assembly 29, which pressure is directed downward against valve 62 and upward against the hammer assembly 29 and the effective lower surface of sleeve 43.

With the valving assembly-of the preferred embodiment,

valve 62 and forces hammer assembly 29 and sleeve 43 upward. Hammer nose 73, support 74 and-spring 75 are carried upward with sleeve 43, forcing valve carrier 68 upward until it contacts the lower surface of nut 67. Sleeve 43 will continue to move upwardly until spring 75 is compressed, at which time the downward pressure on valve 62 and the upward pressure on sleeve 43 will be equal and sleeve 43 will terminate upward movement. Hammer assembly 29 will continue to rise, however, with drilling fluid being evacuated from chamber 21 thereabove through ports 22 and 23. As hammer assembly 29 approaches its uppermost operating position, upwardly facing annular shoulder 51 on bottom sub 29 strikes the lower surface of lug 50 on sleeve 43. This additional upward force on sleeve 43 will be sufiicient to overcome the downward force thereon and sleeve 43, acting through hammer nose 73, spring support 74 and valve carrier 68, will forcevalve 62 upward and out of seating engagement with anvil 57. As valve 62 opens, the pressurized drilling fluid thereabove escapes downward thereabout into passageway 56. This decrease in pressure above valve 62 allows spring 75 and valvecarrier 68 to positively snap valve 62 upwardto the limit of snap ring 76, providing a snap action opening.

While hammer assembly 29 was moving upward, vacuum chamber 32 formed by the opposing annular steps between hammer assembly 29 and mandrel wasincreasing in volume. When the pressure is released beneath hammer assembly 29, hammer assembly 29 begins to fall downward. The vacuum in chamber 32 accelerates this downward movement. This downward acceleration is aided by the hydrostatic mud pressure acting upon the differential upper and lower effective surface areas of the hammer assembly.

In travelling downward, downwardly facing shoulder 38 on thehammer assembly 29 contacts the upper end of sleeve 43, forcing it downward. The combined downward momentum of hammer assembly 29 and sleeve 43 is then transmitted through sleeve 43, hammer nose 73, anvil 57 and connecto 54 to bit 11, delivering a percussive blow thereto.

As sleeve 43 moves downward, snap ring '76 urges downwardly valve carrier 68, which in turn acts through spring 70 to force valve 62 downward into seating engagement with anvil 57. The cycle is then complete and will be repeated as long as circulation is maintained and bit 11 is seated on the bottom of the hole with drill string weight applied thereto.

Since part of the downward force upon hammer assembly 29 is created by hydrostatic pressure, increased mud weight or increased depth will amplify the force of the percussive blow. Increased flow rate of mud at a given depth and mud weight will increase the frequency of the cycle of operation.

An alternate embodiment of the valve carrier means. is shown in FIG. 4, with parts identical to those of the preferred embodiment designated by like numbers. The physical difference between this embodiment and the one above described lies in the construction ofthe valve carrier and the means of securing the valve carrier to sleeve 43. ln this alternate embodiment, a valve carrier 78 is rigidly threaded to the lower end of sleeve 43 and is provided with aplurality of axial drilling fluid'flow passages 79 therethrough and a central axial opening for the slidable receipt of valve stem 63 therein.

valve 62, sleeve 43 and valve carrier 78 will be forced upward until the upper surface .of valve carrier 78 strikes the lower surface of valve stem nut 67. Sleeve 43 will then remain stationary due to the equal upward and downward forces upon the effective lower surface of sleeve 43, as discussed above, until shoulder 51 of bottomhammer sub 28 strikes the bottom surface of lug 55 on sleeve 43. Continued upward-movement of hammer assembly 29 will then be transmitted through sleeve 43 and valve carrier 78 to forcibly unseat valve 62.

During the downward power stroke of hammer assembly 29, the momentum of the hammer assembly will be transmitted through shoulder 38 to sleeve 43 and through valve carrier 78 to anvil 57. Valve spring will urge valve 62 into seating engagement with valve seat 64 on anvil 57, thereby preparing the unit for subsequent cycle.

This description is to be construed as illustrative only and further modifications and alternate embodiments of the invention will be apparent to those skilled in the art in view of this description.

What is claimed is: v

1. In an apparatus for impartingpercussive forces to a drill bit suspended by a drill string in a well bore as an incident of flow of drilling fluid downwardly therethrough, the combination comprising:

a generally tubular housing having means for connection in a drill string at the upper end thereof and arranged for the flow of said drilling fluid downwardly therethrough; a generally tubular shaped mandrel connected to an upper portion of said housing and extending downwardly therein and forming an annular chamber. therebetween;

a hammer assembly having an upper portion slidably mounted about said mandrel and arranged for. axial reciprocal movement therewith in said annular chamber, with said upper portion of said hammer and said mandrel having opposed matching annular shoulders forming a variable volume vacuum chamber, with .the volume of said chamber increasing when said upper portion of said hammer moves upwardly relative to said mandrel, said hammer assembly having a portion arranged for the transmission of percussive forces created by the downward movement of said hammer assembly, and said hammer assembly being characterized by having a downwardly facing end surface which is exposed to the pressure of drilling fluid passing therethrough;

a generally tubular. shaped anvil connected with a lower portion of said housing and having means for connection to said drill string at the lower end thereof, said anvil having a valve seat and being arranged for striking by said hammer assembly during the downward acceleration thereof, to thereby impart percussive forces to said drill bit;

a valve member arranged for seating on said valve seat and having an axial bore therethrough, said bore being of a reduced diameter to thereby restrict the flow of drilling fluid therethrough in the seated condition, and said valve member being arranged for unseating upon upward movement thereof relative to said anvil to thereby relieve the restrictions of fluid flow through said apparatus;

' and, unseating means cooperative with said hammer assembly for moving said valve member to the unseated position during upward travel of said hammer assembly;

whereby, during flow of drilling fluid through said apparatus, said valve member restricts fluid flow therepast in the seated position, thereby increasing fluid pressure thereabove, which pressure is applied to said downwardly facing end surface of said hammer assembly thereby moving said assembly upwardly and therebyvunseating said valve member and releasing said increased pressure, thereby permitting said hammer to move downwardly under the influence of gravity and the force created by said vacuum ch amber,'to thereby impart a percussive blow to said anvil.

2. The invention as claimed in claim 1 wherein:

said hammer assembly has an upwardly facing end surface the effective area of which is greater than the effective area of said downwardly facing end surface of said hammer assembly;

and, said housing includes means for applying fluid pressure external thereof to said upper end surface of said assembly;

whereby, said hammer assembly is urged downwardly by the inbalance of fluid pressures operating in opposite directions thereagainst when said valve member is unseated and said increased pressure thereabove is released.

3. The invention as claimed in claim 1 wherein:

said upper and lower portions of said hammer assembly are arranged for telescoping movement therebetween from retracted to extended positions;

and, said lower portion is operably connected with said unseating means;

said upper and lower portions of said assembly being arranged such that said valve member is unseated when said lower and upper portions reach the extended position and said percussive force is impacted to said anvil when said upperand lower portions of said hammer assembly are in the retracted position.

4. The invention as claimed in claim 1 wherein:

said anvil is arranged for relative axial movement with said housing within predetermined limits;

whereby, upon upward movement of said housing, said anvil moves downwardly relative to said housing and said valve member, thereby unseating said valve member and rendering said tool nonoperable and permitting unrestricted flow of drilling fluid therethrough.

S. The invention as claimed in claim 1 wherein: said bore through said valve member is a central axial bore arranged for the flow of fluid therethrough in both the seated and unseated position of said valve member.

6. The invention as claimed in claim 1 wherein said unseating means includes;

a valve carrier secured to said lower portion of said hammer assembly and slidably secured to said valve for limited axial movement therebetween;

and, compression spring means disposed between said valve carrier and said valve for urging said valve downward relative to said carrier.

7. The invention as claimed in claim 6 wherein:

said valve carrier is rigidly secured to said lower portion of said hammer assembly;

8. The invention as claimed in claim 6 wherein:

said valve carrier is slidably secured to said lower portion of said hammer assembly to allow limited axial movement therebetween;

and, including compression spring means disposed between said valve carrier and said lower portion of said hammer assembly for urging said valve carrier upward relative to said lower portion of said hammer assembly.

9. A drill bit percussor for connection in a drill string comprising:

a tubular housing arranged for connection in a drill string;

' a tubular mandrel coaxially disposed in said housing and depending from the upper end thereof forming an annulus with said housing, said mandrel having a radially outwardly extending upwardly facing annular shoulder thereabout;

a reciprocating piston slidably positioned in said annulus about said mandrel, said piston having a radially inwardly extending downwardly facing annular shoulder thereabout axially positioned adjacent said upwardly facing annular shoulder of said mandrel when said hammer is in its lowermost operation position and forming an annular chamber with said shoulder on said mandrel;

an anvil connected to the lower portion of said housing, said anvil having an axial drilling fluid passageway therethrough and an upwardly facing valve seat about said passageway and means for attaching a drill bit therebelow; -a valve positioned in said housing beneath said hammer,

and, force transmitting means slidably positioned in said housing cooperative with said hammer and said anvil for transmitting downward momentum of said hammer into a percussive blow upon said anvil and cooperative with said hammer and saidvalve for unseating said valve when said hammer approaches its upper limit of travel.

10. A drill bit percussor for connection between a drill collar and a drill bit which is operated by a stream of drilling fluid flowing therethrough, comprising in combination:

a tubular housing arranged for insertion in a drill string;

an anvil mounted in the lower portion of said housing, said anvil having an axial drilling fluid passageway therethrough and a valve seat about said passageway and means for attaching a drill bit therebelow;

. a reciprocating hammer mounted in said housing above said anvil and arranged for limited axial movement in said housing, said hammer having an axial bore therethrough and having an effective upper surface area larger than the effective lower surface thereof, said upper surface being isolated from the stream of drilling fluid flowing downwardly through said percussor;

a valve movably positioned in said housing and arranged to seat with said valve seat of said anvil, said valve having an axial opening therethrough smaller in diameter than said axial bore in said hammer and communicating therewith;

and, force transmitting means slidably mounted in said housing and about the lower portion vof said hammer cooperative with said hammer and said anvil for translating downward momentum of said hammer into a percus sive blow upon said anvil when said hammer approaches the lower limit of travel thereof and cooperative with said hammer and said valve for disengaging said valve from said seat when said hammer approaches the upper limit of travel thereof.

' 11. The invention as claimed in claim 10 wherein said force transmitting means includes:

a sleeve slidably positioned in said housing about the lower portion of said hammer'and arranged for striking contact with said hammer when said hammer approaches its upper and lower limits of movement;

a valve carrier secured to said sleeve and slidably secured to said valve for limited axial movement therebetween; I and, compression spring means disposed between said valve carrier and said valve for urging said valve downward relative to said carrier.

12. The invention as claimed in claim 11 wherein:

said valve carrier is rigidly secured to said sleeve.

13. The invention as claimed in claim 1 1 wherein:

said valve carrier is slidably secured to said sleeve to allow limited axial movement therebetween;

and, including compression spring means disposed between said valve carrier and said sleeve for urging said valve carrier upward relative to said sleeve.

14. The invention as claimed in claim 13 wherein:

said anvil is arranged for limited axially downward movement relative to said housing and said valve when a drill bit fastened to said anvil is positioned above the bottom of the borehole, whereby drilling fluid is allowed to flow downward about said valve and through said valve seat and said percussor is rendered inoperative when said drill bit is not in contact with the formation to be drilled.

U. S. PATIENT OFFICE UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Yatent No. 3, ,3 7 mlwl It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Elva J. Scroggins Column 1, line 48, change "of imbalance" to -of hydrostatic-- Column 3, line 51, change "threadable" to -threadably- Column l, line 48, omit "operational reasons" and substitute -towardtherefor Column 7, line 10, change "inbalance" to imbalance- Signed and sealed this 29th day of February 1972.

(SEAL) Attest:

EDWARD I LFLETCHER, JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In an apparatus for imparting percussive forces to a drill bit suspended by a drill string in a well bore as an incident of flow of drilling fluid downwardly therethrough, the combination comprising: a generally tubular housing having means for connection in a drill string at the upper end thereof and arranged for the flow of said drilling fluid downwardly therethrough; a generally tubular shaped mandrel connected to an upper portion of said housing and extending downwardly therein and forming an annular chamber therebetween; a hammer assembly having an upper portion slidably mounted about said mandrel and arranged for axial reciprocal movement therewith in said annular chamber, with said upper portion of said hammer and said mandrel having opposed matching annular shoulders forming a variable volume vacuum chamber, with the volume of said chamber increasing when said upper portion of said hammer moves upwardly relative to said mandrel, said hammer assembly having a portion arranged for the transmission of percussive forces created by the downward movement of said hammer assembly, and said hammer Assembly being characterized by having a downwardly facing end surface which is exposed to the pressure of drilling fluid passing therethrough; a generally tubular shaped anvil connected with a lower portion of said housing and having means for connection to said drill string at the lower end thereof, said anvil having a valve seat and being arranged for striking by said hammer assembly during the downward acceleration thereof, to thereby impart percussive forces to said drill bit; a valve member arranged for seating on said valve seat and having an axial bore therethrough, said bore being of a reduced diameter to thereby restrict the flow of drilling fluid therethrough in the seated condition, and said valve member being arranged for unseating upon upward movement thereof relative to said anvil to thereby relieve the restrictions of fluid flow through said apparatus; and, unseating means cooperative with said hammer assembly for moving said valve member to the unseated position during upward travel of said hammer assembly; whereby, during flow of drilling fluid through said apparatus, said valve member restricts fluid flow therepast in the seated position, thereby increasing fluid pressure thereabove, which pressure is applied to said downwardly facing end surface of said hammer assembly thereby moving said assembly upwardly and thereby unseating said valve member and releasing said increased pressure, thereby permitting said hammer to move downwardly under the influence of gravity and the force created by said vacuum chamber, to thereby impart a percussive blow to said anvil.
 2. The invention as claimed in claim 1 wherein: said hammer assembly has an upwardly facing end surface the effective area of which is greater than the effective area of said downwardly facing end surface of said hammer assembly; and, said housing includes means for applying fluid pressure external thereof to said upper end surface of said assembly; whereby, said hammer assembly is urged downwardly by the inbalance of fluid pressures operating in opposite directions thereagainst when said valve member is unseated and said increased pressure thereabove is released.
 3. The invention as claimed in claim 1 wherein: said upper and lower portions of said hammer assembly are arranged for telescoping movement therebetween from retracted to extended positions; and, said lower portion is operably connected with said unseating means; said upper and lower portions of said assembly being arranged such that said valve member is unseated when said lower and upper portions reach the extended position and said percussive force is impacted to said anvil when said upper and lower portions of said hammer assembly are in the retracted position.
 4. The invention as claimed in claim 1 wherein: said anvil is arranged for relative axial movement with said housing within predetermined limits; whereby, upon upward movement of said housing, said anvil moves downwardly relative to said housing and said valve member, thereby unseating said valve member and rendering said tool nonoperable and permitting unrestricted flow of drilling fluid therethrough.
 5. The invention as claimed in claim 1 wherein: said bore through said valve member is a central axial bore arranged for the flow of fluid therethrough in both the seated and unseated position of said valve member.
 6. The invention as claimed in claim 1 wherein said unseating means includes; a valve carrier secured to said lower portion of said hammer assembly and slidably secured to said valve for limited axial movement therebetween; and, compression spring means disposed between said valve carrier and said valve for urging said valve downward relative to said carrier.
 7. The invention as claimed in claim 6 wherein: said valve carrier is rigidly secured to said lower portion of said hammer assembly;
 8. The invention as claimed in claim 6 wherein: said valve carrier is slidably secured to said lower portion of said hammer assembly to allow limited axial movement therebetween; and, including compression spring means disposed between said valve carrier and said lower portion of said hammer assembly for urging said valve carrier upward relative to said lower portion of said hammer assembly.
 9. A drill bit percussor for connection in a drill string comprising: a tubular housing arranged for connection in a drill string; a tubular mandrel coaxially disposed in said housing and depending from the upper end thereof forming an annulus with said housing, said mandrel having a radially outwardly extending upwardly facing annular shoulder thereabout; a reciprocating piston slidably positioned in said annulus about said mandrel, said piston having a radially inwardly extending downwardly facing annular shoulder thereabout axially positioned adjacent said upwardly facing annular shoulder of said mandrel when said hammer is in its lowermost operation position and forming an annular chamber with said shoulder on said mandrel; an anvil connected to the lower portion of said housing, said anvil having an axial drilling fluid passageway therethrough and an upwardly facing valve seat about said passageway and means for attaching a drill bit therebelow; a valve positioned in said housing beneath said hammer, said valve being movable to a lower position to seat with said valve seat on said anvil, thereby restricting the downward flow of drilling fluid through said percussor and causing a pressure buildup beneath said hammer for raising said hammer, and movable to an upper position to provide a drilling fluid flow passage past said valve, said valve having a central axial bore therethrough; and, force transmitting means slidably positioned in said housing cooperative with said hammer and said anvil for transmitting downward momentum of said hammer into a percussive blow upon said anvil and cooperative with said hammer and said valve for unseating said valve when said hammer approaches its upper limit of travel.
 10. A drill bit percussor for connection between a drill collar and a drill bit which is operated by a stream of drilling fluid flowing therethrough, comprising in combination: a tubular housing arranged for insertion in a drill string; an anvil mounted in the lower portion of said housing, said anvil having an axial drilling fluid passageway therethrough and a valve seat about said passageway and means for attaching a drill bit therebelow; a reciprocating hammer mounted in said housing above said anvil and arranged for limited axial movement in said housing, said hammer having an axial bore therethrough and having an effective upper surface area larger than the effective lower surface thereof, said upper surface being isolated from the stream of drilling fluid flowing downwardly through said percussor; a valve movably positioned in said housing and arranged to seat with said valve seat of said anvil, said valve having an axial opening therethrough smaller in diameter than said axial bore in said hammer and communicating therewith; and, force transmitting means slidably mounted in said housing and about the lower portion of said hammer cooperative with said hammer and said anvil for translating downward momentum of said hammer into a percussive blow upon said anvil when said hammer approaches the lower limit of travel thereof and cooperative with said hammer and said valve for disengaging said valve from said seat when said hammer approaches the upper limit of travel thereof.
 11. The invention as claimed in claim 10 wherein said force transmitting means includes: a sleeve slidably positioned in said housing about the lower portion of said hammer and arranged for striking contact with said hammer when said hammer approaches its upper and lower limits of movement; a valve carrier secured to said sleeve and slidably secured to said valve for limited axial movement therebetwEen; and, compression spring means disposed between said valve carrier and said valve for urging said valve downward relative to said carrier.
 12. The invention as claimed in claim 11 wherein: said valve carrier is rigidly secured to said sleeve.
 13. The invention as claimed in claim 11 wherein: said valve carrier is slidably secured to said sleeve to allow limited axial movement therebetween; and, including compression spring means disposed between said valve carrier and said sleeve for urging said valve carrier upward relative to said sleeve.
 14. The invention as claimed in claim 13 wherein: said anvil is arranged for limited axially downward movement relative to said housing and said valve when a drill bit fastened to said anvil is positioned above the bottom of the borehole, whereby drilling fluid is allowed to flow downward about said valve and through said valve seat and said percussor is rendered inoperative when said drill bit is not in contact with the formation to be drilled. 